The invention relates to an electric motor with an internal rotor and an external stator with stator coils.
In known electric motors, the stator is formed by a yoke ring and stator pole shanks projecting radially inward therefrom and provided with pole shoes. There is no direct material connection between two adjacent pole shoes in order to lead a maximum of the magnetic flux necessary for the moment set-up through pole shanks and yoke ring. Further, a magnetic short circuit between two pole shoes and thus a worse power density of the motor is thus avoided. In case of an integrally formed stator body, a winding of the stator pole shanks is only possible from the stator center which is difficult or impossible in case of small electric motors in particular and possibly requires high mechanical efforts. To avoid this, it is possible to configure stator pole shanks separately, wind them separately first and subsequently assemble them to form a closed stator. Alternatively, the stator may also comprise an integral basic stator body the stator pole shanks of which are connected, radially inside in the region of the pole shoes, with the respectively adjacent pole shoes by short circuit bridges. The pole shanks may be wound from radially outside. After the windings have been wound, a yoke ring is set upon so that the pole shanks comprise a magnetic connection radially outside.
It is the object of the present invention to facilitate the production of an external stator.
This object is solved, according to the invention, with the features of claims 1 and 6, respectively.
To simplify the winding, the stator comprises an integral basic stator body the stator pole shanks of which are connected radially inside with the respectively adjacent pole shoes by short circuit bridges in the region of the pole shoes. Radially outside, the stator pole shanks are merely connected with each other by a separate yoke ring set thereon. When the yoke ring is detached, the stator pole shanks are accessible from outside so that all the stator pole shanks can be wound from outside. The basic stator body is held together by the short circuit bridges between the adjacent pole shoes. The stator pole shanks can be simply wound from outside so that even a very small external stator can be produced in this manner. The integrity of the basic stator body permits a simple and cost-efficient production. The short circuit bridge between the stator pole shoes consists of the same material as the pole shoes and the stator. Thus, the short circuit bridge creates a magnetic short circuit of the respective stator tooth to both neighboring pole shoes and stator pole shanks, respectively. Although this worsens the power density of the electric motor, the losses can be kept so small that, as a whole, they are of hardly any consequence. Because of the short circuit bridges between the stator pole shoes, a cylinder-like and slot-free inner circumference of the stator can be realized. This lessens the air resistance and the corresponding wind noise, particularly if the rotor rotates fast. Further, due to the magnetic short circuit via the short circuit bridges, the rest moments acting on the rotor are reduced whereby, when the motor is in operation, the excitation of vibrations effected thereby is reduced. Thereby, in turn, the noise emission is reduced and the mechanical wear is reduced.
According to the invention, all the windings on the stator pole shanks are wound with one single continuous winding wire and in one go. The starting and the end point of the winding wire are together on the same contact point. Thereby, the winding of the windings is greatly simplified and accelerated and an approximate faultlessness of the windings and their contacting is secured.
Preferably, two parallel-connected windings of a winding pair can be connected directly with each other and the winding pairs, in turn, can be connected in series with each other. The formation of winding pairs of two stator windings that are to be powered at the same time, respectively, facilitates the winding of all the windings with a single winding wire. If the stator comprises only three pole shanks altogether, the winding of one pole shank can be divided into two partial windings. This principle is also applicable to electric motors with more than three poles. In the case of a stator with six poles, the winding sequence is 1-4-2-5-3-6.
Preferably, the winding wire connections between the winding pairs form a common neutral point. The neutral point is preferably formed by an integral neutral point metal sheet. Thus, all the winding wire connections between two winding pairs lie on a common voltage potential. Thereby, a simple circuit structure and a simple wiring of the control and power electronics for the electronic commutation of the windings is realized.
Preferably, a central body of the neutral point metal sheet is located centrally in a transverse plane, and contact pins for contacting the winding wire connection between two winding pairs axially project therefrom. Thus, a simple integral neutral point metal sheet is formed on which, if necessary, the control and power electronics for commutating the windings can be fixed. The winding wire can be connected with the neutral point metal sheet contact pins by an automatic welding, soldering or crimping procedure. Thus, a simple, cost-efficient and secure contacting of the corresponding winding wire sections with the neutral point metal sheet is realized.
In order to be able to securely fix the neutral point metal sheet in an insulating disc, the contact pins may have barbs excluding an undesired detachment of the neutral point metal sheet from the insulating disc.
According to a preferred embodiment, the smallest cross section of the short circuit bridges is respectively chosen to be so small that maximally 20% of the magnetic flux of a winding are shorted via them. The smallest cross section of the short circuit bridge is chosen such that, on the one hand, a sufficient mechanical stability of the connection between the two respective stator pole shoes is still given, on the other hand, however, the losses permitted because of the magnetic short circuit via them are small.
Preferably, the rotor pole shoes contain rare earths and are configured, for example, as NdFeB rotor. Thereby, the short circuit portion of the short circuit bridge of the entire magnetic flux produced is kept as small as possible and the useful portion of the magnetic flux produced is kept as large as possible.
In the ideal case, the short circuit bridge is so small that it is magnetically saturated for the most time so that its magnetic conductivity tends towards zero when it is saturated. Thereby, the magnetic loss is reliably limited to a low maximum value.
According to a method for manufacturing an external stator with several stator pole shanks respectively supporting a winding, the stator pole shoes allocated thereto being respectively connected with the two adjacent stator pole shoes, the following method steps are provided:
manufacturing the integral basic stator body with the stator pole shanks and the stator pole shoes,
winding all the stator windings on the stator pole shanks from radially outside in one go with one single winding wire, and
setting a separate yoke ring outside onto the stator pole shanks.
With this method, an integral basic stator body is wound in a very simple and cost-effective manner. Thereby, the winding is considerably simplified and accelerated, particularly with basic stator bodies with small inner diameters.